Black tank flush system leaking

[Ford+5er]

Hello, We traded our TT for a 2010 Keystone Montana 3455SA last week. It has a black tank flush hook up in the convienance center. When we hook a hose up to rinse the black tank out, fresh water leaks out into the floor of one of the cabinets under the desk area beside the kitchen. Has anyone experienced this? We're taking it to the dealer for service. The dealer gave us a 30 day plumbing/appliance/electrical warranty. I'm guessing a leak in the feed line into the tank?
That's about the only thing we found wrong through our first weekend camping and trying everything out. We love everything about the 5er, especially all the room.

[cw3jason]

Probably the vacuum breaker. It prevents back flow and uses water pressure to operate, they are known to fail. Also weak water pressure can make them leak as well.

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[dhn]

Like Jason said, it is probably the vacuum breaker/ back flow preventer. If it is over looked when winterizing, it will freeze and crack. Some members here on the forum have replaced them with a brass vacuum breaker that will hold up better than the plastic one. Other members have replaced it with a "Shark Bite" straight through connector and use a Back flow preventer on the end of the hose. The back flow preventer must be on the end of the hose to keep the black tank from contaminating the the water supply. Ether way you should never use the same hose for potable water and to flush the black tank. There are numerous posts here on the forum about the vacuum breaker/back flow preventer that has leaked or flooded campers.

[Jimbeau]

Originally Posted by Ford+5er

Hello, We traded our TT for a 2010 Keystone Montana 3455SA last week. It has a black tank flush hook up in the convienance center. When we hook a hose up to rinse the black tank out, fresh water leaks out into the floor of one of the cabinets under the desk area beside the kitchen. Has anyone experienced this? We're taking it to the dealer for service. The dealer gave us a 30 day plumbing/appliance/electrical warranty. I'm guessing a leak in the feed line into the tank?
That's about the only thing we found wrong through our first weekend camping and trying everything out. We love everything about the 5er, especially all the room.

Had this same thing on my 2005 Challenger. On mine, there was an anti siphon valve that blew out inside the wall behind where that black tank flusher goes in. It was under warranty, but all they did was replace the bad anti siphon valve with a plain elbow and it was fine . Dealer repair guy said it happens all the time on them. One important note is that since your removing the part that stops (black) back flush, just use only a dirty water hose, not drinking water. They cut access panel in wall between TV and shower.

[bzingre]

We experienced the same issue on our Avalanche 340TG. It failed and dumped water into the basement. The vacuum breaker is behind the shower in the wall. I was able to access the pex plumbing behind the shower faucet. It sticks up behind the shower faucet about 18", so in order to pull it down, I had to remove shower faucet in the inside of the TT and the back panel in the basement just behind the utility station (by the water pump). By loosening the fittings at the lower elbow, my wife and I worked together to pull the lines down and access the broken vacuum breaker. I replaced the breaker with an elbow so now it's straight through. I'll use a backflow valve on the outside fitting moving forward. The worst part of the job was reaching behind the shower valves to get the breaker water lines. Entire job took about 45 minutes.

[Desert185]

Best to use a water pressure limiter when flushing the black tank. I have a spare one on a dedicated green hose. One of these days I'll get around to installing the brass replacement one. Probably still use the pressure limiter, though, as there has to be plastic downstream.